CVE-2025-40258 mptcp: fix race condition in mptcp_schedule_work()
A race condition in the Linux kernel MPTCP subsystem can lead to a use-after-free, potentially causing a system crash.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40258?
CVE-2025-40258 is a critical vulnerability in Linux, published on 4 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
mptcp: fix race condition in mptcp_schedule_work()
syzbot reported use-after-free in mptcp_schedule_work() [1]
Issue here is that mptcp_schedule_work() schedules a work, then gets a refcount on sk->sk_refcnt if the work was scheduled. This refcount will be released by mptcp_worker().
[A] if (schedule_work(...)) { [B] sock_hold(sk); return true; }
Problem is that mptcp_worker() can run immediately and complete before [B]
We need instead :
sock_hold(sk); if (schedule_work(...)) return true; sock_put(sk);
[1] refcount_t: addition on 0; use-after-free. WARNING: CPU: 1 PID: 29 at lib/refcount.c:25 refcount_warn_saturate+0xfa/0x1d0 lib/refcount.c:25 Call Trace: <TASK> __refcount_add include/linux/refcount.h:-1 [inline] __refcount_inc include/linux/refcount.h:366 [inline] refcount_inc include/linux/refcount.h:383 [inline] sock_hold include/net/sock.h:816 [inline] mptcp_schedule_work+0x164/0x1a0 net/mptcp/protocol.c:943 mptcp_tout_timer+0x21/0xa0 net/mptcp/protocol.c:2316 call_timer_fn+0x17e/0x5f0 kernel/time/timer.c:1747 expire_timers kernel/time/timer.c:1798 [inline] __run_timers kernel/time/timer.c:2372 [inline] __run_timer_base+0x648/0x970 kernel/time/timer.c:2384 run_timer_base kernel/time/timer.c:2393 [inline] run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403 handle_softirqs+0x22f/0x710 kernel/softirq.c:622 __do_softirq kernel/softirq.c:656 [inline] run_ktimerd+0xcf/0x190 kernel/softirq.c:1138 smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
Which versions are affected by CVE-2025-40258?
How do I fix CVE-2025-40258?
Apply the vendor's patch.
Is CVE-2025-40258 being exploited?
There is no known exploitation of CVE-2025-40258 in the wild and no public exploit code.
Sources
Also known as AZL-71380, BELL-CVE-2025-40258, DEBIAN-CVE-2025-40258, GHSA-86fp-6jqc-qg25, ROOT-OS-DEBIAN-11-CVE-2025-40258, ROOT-OS-DEBIAN-12-CVE-2025-40258 and 4 more.